The present invention relates in general to shaft linings and in particular to a new and useful method and device for lining a shaft which extends through a water bearing formation.
Methods of sinking shafts through water-bearing formations are known. Frequently the freezing method is employed in which, at the location where the shaft is to be sunk, heat is removed from the water-bearing region up to the freezing temperature for water. A frozen jacket is thereby produced whose axis coincides with that of the shaft to be provided. Within this jacket, the shaft can be excavated under the protection of the frozen wall as in a dry formation, and made watertight. The freezing method, however, is relative expensive in labor and installation, since freezing tubes must be driven at the perimeter of the future shaft through the aquiferous layers down into an underlying impermeable formation. In addition, fall pipes must be suspended in the freezing tubes and continuously supplied with a low-temperature fluid as the cooling agent. This requires the installation of a refrigerating machine on the surface.
A shaft boring method is also known in which a bore hole of larger diameter and without lining is driven through the aquifer zone and an excess pressure relative to the hydrostatic pressure of the surrounding water is produced within the bore. This excess pressure is produced by a column of liquid reaching up to the bore mouth, for example a column of slushed fluid, such as clay mud-laden flush water. The pressure of the fluid column retains the surrounding water. In this prior art method, the lining structure is assembled on the surface, above the finish-bored shaft hole, and then immersed into the hole which is filled with the mud-laden fluid. The lining, as a rule, is a double-walled steel tube assembled of annular tube lengths filled with concrete and provided with a false bottom. The steel tube plunges into the clay-laden fluid under its own weight, with the inner space of the tube being filled with water as ballast. The clay-laden fluid is thereby displaced upwardly. Upon reaching the final depth, the steel tube is plumb-lined to the center of the bore hole and the annular space between the tube and the wall of the hole is filled with concrete. Then, the water ballast is pumped out, the false bottom is removed and boring may continue.
The shaft boring method is preferred to the freezing method for reasons of economy, because boring is much faster than conventional digging and, in addition, the refrigerating equipment is omitted. Only, the plunging of the lining which is assembled on the surface is very problematic. That is, the double-walled steel tube filled with concrete is extremely heavy and the weight is yet considerably increased by the water ballast. Therefore, it frequently happens that the boring derrick set up over the shaft mouth is not sufficiently dimensioned for the plunging operation and may collapse. This endangers the crew and may seriously damage the bore, up to its complete destruction. But even without such mishaps, the plumb-lining alone, which is needed for centering of a lowered lining, is extremely complicated and difficult, because of the excessive weight to be handled. The invention design eliminates these drawbacks.